linux-kernel - Re: [PATCH 2/3] ASoC: dt-bindings: sama7g5-pdmc: add microchip,startup-delay-us binding

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Message-ID: <fd2f372f-4a1c-72c0-574d-1d5ef99dbdbc@linaro.org>
Date:   Thu, 16 Feb 2023 11:18:16 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Claudiu.Beznea@...rochip.com, lgirdwood@...il.com,
        broonie@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, lars@...afoo.de, perex@...ex.cz,
        tiwai@...e.com, Nicolas.Ferre@...rochip.com,
        alexandre.belloni@...tlin.com
Cc:     alsa-devel@...a-project.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/3] ASoC: dt-bindings: sama7g5-pdmc: add
 microchip,startup-delay-us binding

On 16/02/2023 11:15, Claudiu.Beznea@...rochip.com wrote:
> On 16.02.2023 12:04, Krzysztof Kozlowski wrote:
>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>
>> On 14/02/2023 17:14, Claudiu Beznea wrote:
>>> Add microchip,startup-delay-us binding to let PDMC users to specify
>>> startup delay.
>>>
>>> Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
>>> ---
>>>  .../devicetree/bindings/sound/microchip,sama7g5-pdmc.yaml   | 6 ++++++
>>>  1 file changed, 6 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/sound/microchip,sama7g5-pdmc.yaml b/Documentation/devicetree/bindings/sound/microchip,sama7g5-pdmc.yaml
>>> index c4cf1e5ab84b..9b40268537cb 100644
>>> --- a/Documentation/devicetree/bindings/sound/microchip,sama7g5-pdmc.yaml
>>> +++ b/Documentation/devicetree/bindings/sound/microchip,sama7g5-pdmc.yaml
>>> @@ -67,6 +67,12 @@ properties:
>>>      maxItems: 4
>>>      uniqueItems: true
>>>
>>> +  microchip,startup-delay-us:
>>> +    description: |
>>> +      Specifies the delay in microseconds that needs to be applied after
>>> +      enabling the PDMC microphones to avoid unwanted noise due to microphones
>>> +      not being ready.
>>
>> Is this some hardware delay? Or OS? If OS, why Linux specific delay is
>> put into DT?
> 
> It's the delay used in software workaround that IP needs to filter noises.

Then this sounds like OS? Linux related properties usually do not belong
to DT.

> The IP is not fully featured to do this kind of filtering on its own thus
> this software workaround. This delay may depend on used microphones thus
> for different kind of setups (PDMC + different microphones) I introduced
> this in DT.

I understand your driver needs delay and I am not questioning this. I am
questioning why this is suitable for DT?


Best regards,
Krzysztof